Objective:To test Candonocypris novaezelandiae(Baird)(C.novaezelandiae),sub-class Ostracoda,obtained from the Nile,Egypt for its predatory activity on snail,Biomphalaria alexandrina(B.alexandrina),intermediate host of Schistosoma mansoni(S.mansoni)and on the free-living larval stages of this parasite(miracidia and cercariae).Methods:The predatory activity of C.novaezelandiae was determined on B.alexandrina snail(several densities of eggs,newly hatched and juveniles).This activity was also determined on S.mansoni miracidia and cercariae using different volumes of water and different numbers of larvae.C.novaezelandiae was also tested for its effect on infection of snails and on the cercarial production.Results:C.novaezelandiae was found to feed on the eggs,newly hatched and juvenile snails,but with significant reduction in the consumption in the presence of other diet like the blue green algae(Nostoc muscorum).This ostracod also showed considerable predatory activity on the free-living larval stages of S.mansoni which was affected by certain environmental factors such as volume of water,density of C.novaezelandiae and number of larvae of the parasite.Conclusions:The presence of this ostracod in the aquatic habitat led to significant reduction of snail population,infection rate of snails with schistosme miracidia as well as of cercarial production from the infected snails.This may suggest that introducing C.novaezelandiae into the habitat at schistosome riskv sites could suppress the transmission of the disease. Objective: To test Candonocypris novaezelandiae (Baird) (C. novaezelandiae), sub-class Ostracoda, obtained from the Nile, Egypt for its predatory activity on snail, Biomphalaria alexandrina (B. alexandrina), intermediate host of Schistosoma mansoni (S.mansoni ) and on the free-living larval stages of this parasite (miracidia and cercariae). Methods: The predatory activity of C. novaezelandiae was determined on B.alexandrina snail (several densities of eggs, newly hatched and juveniles) .This activity was also determined on S.mansoni miracidia and cercariae using different volumes of water and different numbers of larvae. C. novaezelandiae was also tested for its effect on infection of snails and on the cercarial production. Results: C. novaezelandiae was found to feed on the eggs , newly hatched and juvenile snails, but with significant reduction in the consumption in the presence of other diet like the blue green algae (Nostoc muscorum) .This ostracod also showed considerable predatory activity on the free-living l arval stages of S.mansoni which was affected by certain environmental factors such as volume of water, density of C. novaezelandiae and number of larvae of the parasite. Confc: The presence of this ostracod in the aquatic habitat led to significant reduction of snail population , infection rate of snails with schistosme miracidia as well as of cercarial production from the infected snails. This may suggest that introducing C. novaezelandiae into the habitat at schistosome riskv sites could suppress the transmission of the disease.